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  • Magnetic properties of GaAs:Mn self-assembled nanostructures grown at relatively high-temperature by Molecular Beam Epitaxy
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-12-10
    A. del Rio-de Santiago, C.F. Sánchez-Valdés, J.L. Sánchez Llamazares, M.A. Vidal, V.H. Méndez-García, M. López-López, E. Cruz-Hernández

    We report the influence of the Mn atomic concentration (at. %) on the nanostructures formation and magnetic properties of GaAs:Mn layers grown by Molecular Beam Epitaxy at a relatively high substrate temperature of 530 °C varying the nominal Mn at. % content from 0.01 to 0.2. It is shown that by modifying the Mn at. % different kind of nanostructures, ranging from 2D (such as islands and surface corrugation) to 3D microleave- and nanowire-like arrays, form on the surface layer. Samples produced with Mn contents ranging from 0.02 to 0.20 at. % show a significant room temperature ferromagnetic response that is attributed to the formation of MnAs nanocrystals as confirmed from X-ray diffraction analysis and magnetization measurements. The influence of MnAs clusters on the formation of the nanostructures observed is discussed.

    更新日期:2018-12-11
  • Dynamic Magneto-optical Inversion in Magnetic Fluid using NanoMOKE
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-12-11
    Komal Jain, Saurabh Pathak, Prashant Kumar, Arjun Singh, RP Pant

    Systematic inversion of optical anisotropy with magnetic field sweep (0-5000Gauss) has been observed at a critical concentration in the monodispersed magnetic fluids using NanoMOKE III. This experimental technique is significantly novel method to investigate the optical anisotropy of magnetic nano-suspensions with the time-varying magnetic field. In this work, we report a detailed experimental investigation on the field dependent magneto-optical behaviour of dilute water dispersed Fe3O4 based magnetic fluid. Magnetic fluid shows tunable magneto-optical properties which primarily depends on parameters such as, particle concentration, composition and carrier medium. We have observed a systematic inversion in optical anisotropy at critical concentration for a Fe3O4 magnetic fluid with strong spatial dependence. The observed tuneable magneto-optical phenomena have been correlated to the net effect of the structuration process, electronic transitions and gravitational force in the presence magnetic field. This phenomenon leads to the development of two particle size distribution, negative optical activity initially and strong spatial dependence respectively. The present results provide a strong correlation with theoretical models presented to expound the dependency of various parameters on magneto-optical inversion behaviour of magnetic fluids.

    更新日期:2018-12-11
  • Pressure dependence of the magnetic properties and phase diagram of HoCo12B6 ferrimagnetic compound
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-12-11
    L.V.B. Diop, Z. Arnold, J. Kamarád, O Isnard

    The magnetic properties of HoCo12B6 ferrimagnetic compound are investigated versus the magnetic field, temperature and pressure. The magnetic phase diagram exhibits three remarkable temperatures: the ordering temperature TC, the spin reorientation temperature TSR and the compensation temperature TCOMP at 147 K, 76 K and 47 K respectively. In HoCo12B6 intermetallic system the spontaneous magnetization resulting from the antiparallel coupling of the magnetic moments of Ho and Co sublattices is pressure insensitive at lowest temperatures whereas it decreases with pressure at temperature range above TSR. The mean Co magnetic moment is small (< 0.5µB) in the studied compound and exhibits a weak pressure dependence. In addition, significant pressure effects have been observed on both the spin reorientation transition and the Curie temperatures. A value of dTC/dp = -3.5±0.4 K GPa-1 is dominated by the Co sublattice contribution. The spin reorientation transition temperature is also found to decrease versus pressure dTSR/dp = -4.2±0.4 K GPa-1. The compensation temperature where the Ho and Co sublattices have the same magnitude but opposite direction does not vary significantly with applied pressure in the investigated pressure range (up to 1GPa). The results of pressure dependence of the magnetic properties are compared to earlier results on other R-Co-B borides. HoCo12B6 compound confirmed the remarkably high volume stability of the magnetic properties of the RCo12B6 compounds with the itinerant character of magnetism and low values of both the TC and magnetization.

    更新日期:2018-12-11
  • Size-Dependent Structural and Magnetic Properties of Disordered Co2FeAl Heusler Alloy Nanoparticles
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-12-11
    Aquil Ahmad, Srimanta Mitra, S.K. Srivastava, A.K. Das

    Co2FeAl (CFA) nanoparticles (NPs) of different sizes were synthesized by chemical route. The effect of the size of NPs upon the structure and magnetization compared to its bulk counterpart was investigated. The structure and composition were determined from X-ray diffraction (XRD) and electron microscopy. XRD analysis shows that the samples are having single (A2-type) disordered phase. Magnetization measurements suggest that the samples are soft ferromagnetic in nature with very low coercivity. Enhanced magnetic properties like saturation magnetization, coercive force, retentivity, and Curie-temperature are observed with a decrease in particle size. The effect of particle size on hysteresis losses is also discussed. The smallest particles of size 16 nm exhibited the highest saturation magnetization and transition temperature of 180.73 emu/g and 1261 K, respectively. The origin of enhancement in magnetization of Co2FeAl nano-alloy is attributed to the strong Co-Co exchange interaction due to disorder present in the systems.

    更新日期:2018-12-11
  • Coercivity enhancement and magnetic property evaluation of Bi doped Mn2Sb
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-12-11
    Kritika Anand, Nithya Christopher, Jagdish Kumar, Anurag Gupta, Nidhi Singh

    Mn2Sb is a well-known ferrimagnetic material, which has been investigated thoroughly to understand the effect of doping on its magnetic properties. Present work reports the synthesis of Bi doped Mn2Sb employing arc-melting and melt spinning followed by characterization with a view to establish a correlation in the structure and magnetic properties. Bi doping in Mn2Sb lattice produces a significant change in the latter’s magnetic properties, giving rise to a saturation magnetization of 27.2 emu/g (27.2 Am2/Kg) and a high coercivity value of 3.4 kOe (279.2 kA/m), in comparison to Mn2Sb, which has a coercivity of 0.1 kOe (7.96 kA/m). Theoretical studies were carried out to understand the changes in magnetic properties. Ab-initio electronic and atomic structure calculations show that Bi atom occupies equally the MnI and MnII sites and this leads to ferromagnetic ordering, which results in enhancement of the saturation magnetisation. The coercivity mechanism has also been studied in detail; the large coercivity is attributed to the nucleation mechanism achieved via the inclusion of diamagnetic Bi particles in Mn2Sb.

    更新日期:2018-12-11
  • Unexpected large transverse magneto-optic Kerr effect at quasi-normal incidence in magnetoplasmonic crystals
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-12-11
    R. Cichelero, M.A. Oskuei, M. Kataja, S.M. Hamidi, G. Herranz

    We investigate the transverse magneto-optic Kerr effect (TMOKE) of magnetoplasmonic crystals grown on top of commercial optical disks. From full angle-resolved scans we can identify Wood’s anomalies related to the excitation of plasmons of different orders. From these maps we also detect a wide range of wavelengths and angles of incidence for which the TMOKE signal is increased due to the interaction of light with surface propagating plasmons. Remarkably, conditions are established for unexpectedly large responses at quasi-normal incidence, where, by fundamental symmetry reasons, the intrinsic TMOKE should be vanishingly small. The key towards this unexpected outcome is to engineer the geometry of magnetoplasmonic crystals, so that first-order plasmon dispersion lines run up towards quasi-normal angles of incidence. These results provide general rules for magneto-optic enhancement and, in particular, show the potential of standard commercial disks as platforms for enhanced magneto-optic devices.

    更新日期:2018-12-11
  • Microstructure and improved properties of sintered Nd-Fe-B magnets by grain boundary diffusion of non-rare earth
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-12-11
    W. Chen, Y.L. Huang, J.M. Luo, Y.H. Hou, X.J. Ge, Y.W. Guan, Z.W. Liu, Z.C. Zhong, G.P. Wang

    Al film, which was coated in sintered Nd-Fe-B magnets prepared by magnetron sputtering, was employed for grain boundary diffusion source. Effects of the grain boundary diffusion processes (GBDP) on the microstructure evolution and properties were investigated in detail. Through grain boundary diffusion processes, the highest coercivity of 1184 kA/m and maximum energy product of 238 kJ/m3 could be obtained, increasing by 21.8 % and 3.9 %, respectively, compared with the initial magnet. Meanwhile, our results showed that fine, uniform and continuous intergranular phase induced by Al diffusion, was the main reason for properties improvement, while a weak ferromagnetic phase and the vague interface between main phase and RE-rich phase should be responsible to the deterioration of coercivity when the diffused temperature exceed 600°C. Besides, the corrosion resistance of Al-diffused magnets was also greatly improved, owing to the fact that the Al element could promote the electrochemical potential of RE-rich phase and the more thin, continuous intergranular phase would also narrow the corrosion channel.

    更新日期:2018-12-11
  • Study of band structure of iron nitrides by angle resolved photoemission spectroscopy
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-12-11
    Henan Fang, Junlin Chen, Ying Li, Xiang Peng, Zhikuo Tao

    The band structure of Fe-N film is studied by angle resolved photoemission spectroscopy. It is found that the 3d band of Fe-N film disappears due to the hybridization of Fe 3d states and N 2p states. The result can account for the less ferromagnetism and conductivity of Fe-N film when compared with those of Fe film. This finding indicates that the high content of nitrogen can significantly change the band structure of iron nitrides, which exceeds the conventional theoretical prediction. The present work may evoke the re-recognization to the effect of coupling of Fe and N, and promote the further research of band structure of iron nitrides.

    更新日期:2018-12-11
  • Magnetization sign reversal, Exchange bias, and Griffiths-like phase in orthorhombic perovskite Pr2FeMnO6
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-12-11
    Aswathi Kaipamangalath, Jasnamol Pezhumkattil Palakkal, Manoj RaamaVarma

    The perovskite Pr2FeMnO6 has been synthesized by citrate-gel combustion method. The material has an orthorhombic crystal structure with Pbnm space group. The presence of Fe3+ and Mn3+ cations in the material are confirmed by XPS analysis. A magnetization sign reversal is observed for the material at low-temperatures in low applied magnetic fields. When the applied field or temperature is increased, the negative magnetization got diminished. Such a sign reversal of magnetization is observed for the material as a result of the interaction between components of paramagnetic Pr3+ and Mn3+ moments opposite to the component of the ferromagnetic Fe3+ moment or the anti-aligned Fe –rich regions to that of Mn-rich regions containing with Pr3+. Negative exchange bias is also exhibited by Pr2FeMnO6 below 200 K which can be ascribed to the Dzyaloshinskii-Moriya interaction and magnetic exchange anisotropy. A high-temperature magnetic transition at TC = 576 K is identified for the material from the thermomagnetic data. From the detailed analysis of the thermomagnetic data, the presence of ferromagnetic short-range correlations is observed far above the TC, which suggests a Griffiths-like phase with Griffiths temperature at TG = 681 K.

    更新日期:2018-12-11
  • Rod-like particles of silica-coated maghemite: synthesis via akaganeite, characterization and biological properties
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-12-11
    Pavel Veverka, Mariia Pashchenko, Lenka Kubíčková, Jarmila Kuličková, Zdeněk Jirák, Radim Havelek, Karel Královec, Jaroslav Kohout, Ondřej Kaman

    A multistep procedure, employing akaganeite FeO(OH,Cl) as a precursor, was developed for the preparation of rod-like maghemite particles for medical applications. At first, akaganeite rods with length of several hundred nm and width of ≈85 nm were prepared under hydrothermal conditions and were subsequently coated with mesoporous silica. Such coating enabled to maintain the shape of rods during the following steps that involved structural transformation of akaganeite to maghemite, i. e. γ-Fe2O3. Then the original protective coating was removed by alkaline leaching, bare maghemite rods were isolated, and their structure and ferrimagnetic order were characterized by X-ray diffraction, TEM inspection, Mössbauer spectroscopy and SQUID magnetometry. The magnetization of the bare maghemite rods, that were formed by elongated clusters of ≈10–20 nm crystallites, made 47.0 and 41.7 Am2/kg in magnetic field of 3 T at 5 and 300 K, respectively. The hysteresis loops of both the bare and coated products at 300 K and ZFC/FC studies showed that the maghemite particles were largely blocked at room temperature in spite of the small size of crystallites. Finally, the particles were equipped with standard silica coating for biological studies. An evaluation of cytotoxicity of this silica-coated product was performed on two cell lines, namely A549 and MCF-7. The viability of cells incubated with particles at the concentration of 0.10, 0.21 and 0.42 mmol(Fe)/L was determined after 24 h and 48 h of incubation, and the values normalized to the viability of negative control were generally higher than 95 %. Moreover, the real-time monitoring of cell adhesion, proliferation, and cytotoxicity by an xCELLigence system during 72 h of the incubation with particles revealed only some decrease of the cell index for the MCF-7 cells at the high concentration.

    更新日期:2018-12-11
  • Microstructure, magnetic properties and thermal conductivity of LaFe11.2Si1.8/Ta magnetocaloric composites
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-12-11
    Qiming Wu, Naikun Sun, Xiangjie Wang, Lingwei Li

    The LaFe11.2Si1.8/Ta composite materials with Ta contents of 4, 8 and 12 wt.% were fabricated. The crystal structure, component, magnetocaloric property and thermal conductivity of the composite materials were detected. It is found that the addition of Ta does not change the Curie temperature and magnetic phase transition feature of LaFe11.2Si1.8/Ta composite materials. The maximal magnetic entropy change (-ΔSMmax) are 11.17, 10.71 and 10.56 J/kg K for Ta contents of 4, 8 and 12 wt.% under a magnetic field change of 0-7 T, respectively. Correspondingly, the values of relative cooling power (RCP) are 394.55, 402.91 and 408.20 J/kg. The thermal conductivity (λ) improves remarkably with increasing Ta content, and the values of λ are evaluated to be 4.49(6), 5.56(3) and 7.10(2) W/m∙K for LaFe11.2Si1.8/Ta with Ta contents of 4, 8 and 12 wt.% at their own Curie temperatures, respectively.

    更新日期:2018-12-11
  • Exploring the Electronic and Magnetic Properties of New Metal Halides from Bulk to Two-Dimensional Monolayer: RuX3 (X=Br, I)
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-12-11
    Fatih Ersan, Erol Vatansever, Sevil Sarikurt, Yusuf Yüksel, Yelda Kadioglu, H. Duygu Ozaydin, Olcay Üzengi Aktürk, Ümit Akıncı, Ethem Aktürk

    Theoretical and experimental studies present that metal halogens in MX3 forms can show very interesting electronic and magnetic properties in their bulk and monolayer phases. Many MX3 materials have layered structures in their bulk phases, while RuBr3 and RuI3 have one-dimensional chains in plane. In this paper, we show that these metal halogens can also form two-dimensional layered structures in the bulk phase similar to other metal halogens, and cleavage energy values confirm that the monolayers of RuX3 can be possible to be synthesized. We also find that monolayers of RuX3 prefer ferromagnetic spin orientation in the plane for Ru atoms. Their ferromagnetic ground state, however, changes to antiferromagnetic zigzag state after U is included. Calculations using PBE+U with SOC predict indirect band gap of 0.70 eV and 0.32 eV for the optimized structure of RuBr3 and RuI3, respectively. Calculation based on the Monte Carlo simulations reveal interesting magnetic properties of RuBr 3 , such as large Curie temperature against RuI 3 , both in bulk and monolayer cases. Moreover, as a result of varying exchange couplings between neighboring magnetic moments, magnetic properties of RuBr 3 and RuI 3 can undergo drastic changes from bulk to monolayer. We hope our findings can be useful to attempt to fabricate the bulk and monolayer of RuBr3 and RuI3.

    更新日期:2018-12-11
  • Microstructure and magnetic properties of multi-main-phase Ce-Fe-B spark plasma sintered magnets by dual alloy method
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-12-11
    Qingzheng Jiang, Lunke He, Weikai Lei, Qingwen Zeng, Sajjad Ur Rehman, Lili Zhang, Renhui Liu, Jiajie Li, Shengcan Ma, Zhenchen Zhong

    Ce-Fe-B spark plasma sintered (SPSed) magnets prepared with different ratio of alloys of Ce-Fe-B and Pr-Nd-Fe-B by dual alloy method are investigated in this paper. As expected, the remanent magnetization Jr, coercivity Hci and maximum energy product (BH)max of SPSed magnets increase obviously with increasing weight percentage of Pr-Nd-Fe-B alloy. The magnetic properties of Jr = 0.71 T, Hci = 915 kA/m, (BH)max = 72 kJ/m3 are obtained for the SPSed magnets with 80 wt% Pr-Nd-Fe-B alloy. There are three Curie temperatures in this type magnet, which implies the coexistence of three hard magnetic phases. The second Curie temperature depends on the Pr-Nd-Fe-B content. With increasing Pr-Nd-Fe-B alloy content, the volume fraction and width of coarse grain zone decrease. It is shown by the microstructure analysis that the rare earth elements diffuse during sintering process resulting in the formation of Pr-Nd-Ce-Fe-B hard magnetic phase. The intergranular exchange coupling strength is enhanced with increasing Pr-Nd-Fe-B content. The present research may be a potential reference for further research and development of this type Ce-containing nanocrystalline permanent magnetic materials.

    更新日期:2018-12-11
  • Significant Improvement of the 2:14:1 Phase Formability and magnetic properties of Multi-phases RE-Fe-B magnets with La substitution for Ce
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-12-11
    Qi Shi, Ying Liu, Jun Li, Wei Zhao, Renquan Wang, Xi Gao

    In this paper, the Ce-Fe-B and (La, Ce)-Fe-B strips were prepared by strip-casting technique and the multi-phases RE-Fe-B (RE=La, Ce, Pr and Nd) magnets were fabricated by dual-alloy method with (Pr, Nd)-Fe-B alloy. The effects of La substitution for Ce on the microstructure of Ce-Fe-B strip-casting alloy were investigated, especially for the formability of 2:14:1 phase. The results showed that the proportion of RE2Fe14B phase significantly increased from 0.0% to 48.0% and the CeFe2 phase drastically decreased from 67.1% to 38.1% with La substitution for 35wt.% Ce in Ce-Fe-B strip-casting alloy. It could be attributed to the enlarged temperature gap between the formation of 2:14:1 phase and Ce2Fe17 phase, which was beneficial for the formability of 2:14:1 phase. Owing to the rise of the proportion of the 2:14:1 phase, the remanence (Br) and maximum energy product ((BH)max) of dual-alloy magnets increased from 11.49 kGs, 28.68 MGOe to 12.38 kGs, 34.76 MGOe with respect to 32.0wt.% Ce or La-Ce substitution content for Pr-Nd, respectively. Meanwhile, the coercivity (Hcj) slightly decreased from 6.49 kOe to 6.16 kOe, which was caused by the decrease of HA (54.09 kOe → 42.37 kOe) and the deterioration of microstructure of the magnet. This work indicated that the cost-effective La-contained RE-Fe-B permanent magnets could be prepared by dual-alloy method.

    更新日期:2018-12-11
  • Improvement of DyF3 diffusion efficiency in sintered Nd-Fe-B magnets by stack diffusion technology
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-12-11
    Xiao Yang, Shuai Guo, Guangfei Ding, Xuejing Cao, Jiling Zeng, Jie Song, Aru Yan

    The diffusion efficiency of DyF3 is significantly enhanced by using a novel stack procedure. In the stack procedure, the magnets place one on top of the other to ensure the contact surface does not expose outside directly. During the diffusion process, DyF3 first convertes to NdF3, then NdF3 reacts with trace oxygen in the cavity to form NdOF that makes more F atoms diffuse into magnet, which is detrimental to the enhancement of coercivity. But through the stack diffusion technology, the tight contract between the upper and bottom surface of magnets suppresses the oxidation of NdF3 as much as possible to prevent the formation of NdOF. Thus, less F diffusion into magnets, better Dy distribution and higher coercivity increment are obtained. After 10 h diffusion, the coercivity of magnet under stack diffusion increases from 15.45 kOe to 17.47 kOe with 0.28 wt.% Dy consumption and the increment is almost twice that of magnet treated in traditional diffusion.

    更新日期:2018-12-11
  • Comment on “Magnetic Compton scattering study of Laves phase ZrFe2 and Sc doped ZrFe2: Experiment and Green function based relativistic calculations” by Bhatt et al.
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-07-11
    G. Kontrym-Sznajd, S.B. Dugdale

    We show how to calculate isotropic Compton profiles from sets of profiles along so-called “special directions” in the Brillouin zone computed from density-functional theory calculations, with reference to a recent paper by Bhatt et al. We present the correct formula and demonstrate the power of special directions, highlighting the importance of carefully choosing directions and using the correct weights in obtaining accurate isotropic profiles.

    更新日期:2018-12-10
  • Vortex and double-vortex nucleation during magnetization reversal in Fe nanodots of different dimensions
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-12-10
    Andrea Ehrmann, Tomasz Blachowicz

    Magnetic nanodots are of high technological importance in diverse storage and spintronics applications, especially in bit patterned media. Magnetization reversal in such nanodots typically occurs either by coherent rotation of the magnetization or along a vortex state. Other mechanisms of magnetization reversal are scarcely described in the literature. Understanding and predicting the magnetization reversal processes, however, is of utmost importance due to the varying stray fields in the different states under evolution, influencing neighboring nanodots in an array or matrix-like structure. Besides, the stability of vortex states against magnetic field changes – which corresponds to typically broad field ranges with reversible modifications of the magnetic state – influences the robustness of magnetically stored information as well as the necessary external fields for writing new information. Here we report on micromagnetic simulations on nanodots with 10 different, representative diameters and 10 dot thicknesses, respectively, giving rise to 8 possible magnetization reversal processes and suggesting the preconditions for the nucleation and propagation of one or two vortices in cylindrical iron disks. We show the impact of the dimensions and aspect ratios on all phases of magnetization reversal. This study results in a phase diagram of the different magnetization reversal processes.

    更新日期:2018-12-10
  • First-principles study of the magnetic and electronic properties of ACr2As2 (A = Sr, Ba)
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-12-10
    Wenqi Zhou, Ping Hu, Shuwei Li, Shuxiang Wu

    We report a detailed density functional theory investigation for ACr2As2 (A = Sr, Ba), which are isostructural to their iron counterparts AFe2As2, parent compounds of iron-based superconductors. The calculated results for these two compounds are quite similar, indicating that the A site ions have only a relatively small impact on the magnetic and electronic structures. It is found that both ACr2As2 favor an itinerant antiferromagnetic ground state with G-type spin arrangement, and possess a sizable magnetocrystalline anisotropy energy with the easy axis directed along the c axis perpendicular to the CrAs plane. Furthermore, the optimized lattice constants and internal atomic parameter of ACr2As2 are found to be sensitive to magnetic ordering, which implies the presence of a magnetostructural coupling effect.

    更新日期:2018-12-10
  • Configurational Entropy for Skyrmion-like Magnetic Structures
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-12-10
    D. Bazeia, D.C. Moreira, E.I.B. Rodrigues

    In this work we explore the relationship between two ideas recently introduced in the literature. The first one deals with a quantity related to the informational contents of solutions of spatially localized structures, and the second consists of obtaining analytical solutions to describe skyrmion-like structures in magnetic materials. In particular, we use the topological charge density to extract information on the configurational entropy of the magnetic structure.

    更新日期:2018-12-10
  • Insight into electronic, magnetic and optical properties of magnetically ordered Bi2Fe4O9
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-12-10
    Shaan Ameer, Kajal Jindal, Monika Tomar, Pradip K. Jha, Vinay Gupta

    Non-collinear antiferromagnetic (AFM) spin structure is imposed in Bi2Fe4O9 to study the electronic and magnetic properties of magnetically ordered Bi2Fe4O9 using first principles. Electronic properties carried out for both ferromagnetic (FM) and antiferromagnetic (AFM) orderings in Bi2Fe4O9 suggest that FM Bi2Fe4O9 is a semiconductor with an indirect optical bandgap of 1.732 eV, whereas, AFM Bi2Fe4O9 is a multiband semiconductor. The influence of different magnetic orderings on the electronic properties of Bi2Fe4O9 are studied in detail. The linear optical response of FM Bi2Fe4O9 is also investigated.

    更新日期:2018-12-10
  • Response to “Comment on: The effect of magnetic field induced aggregates on ultrasound propagation in aqueous magnetic fluid [J. Magn. Magn. Mater. 431 (2017) 74–78]”
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-08-01
    Kinnari Parekh, R.V. Upadhyay

    Reply to comments on our paper entitled ‘The effect of magnetic field induced aggregates on ultrasound propagation in aqueous magnetic fluid’ [J. Magn. Magn. Mater. 431 (2017) 74–78]. We show here that comments does not stand valid.

    更新日期:2018-12-09
  • Comment on: “The effect of magnetic field induced aggregates on ultrasound propagation in aqueous magnetic fluid” [J. Magn. Magn. Mater. 431 (2017) 74–78]
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-08-06
    Victor V. Sokolov

    It is pointed out that a recent article (Parekh and Upadhyay, 2017) is conceptually wrong. I have shown that authors (Parekh and Upadhyay, 2017) to obtained unreasonably good agreement between the calculated and the experimental data.

    更新日期:2018-12-09
  • Two Phase Flow of Blood through a Circular Tube with Magnetic Properties
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-08-30
    Azhar Ali Zafar, Nehad Ali Shah, Ilyas Khan

    In this paper, two-phase flow of blood is considered through a circular tube along with magnetic properties. The tube is considered as a circular cylinder form and the blood is flowing through it under the influence of uniform magnetic field and an external oscillating pressure gradient. Exact solutions for the fluid and magnetic particles velocities are obtained by means of integral transforms. The velocity of the fluid is presented as a sum of post transient and transient solutions. Moreover, a semi-analytical solution based on the Bessel equation and Tzou’s algorithm for the inverse Laplace transform is obtained. A comparison among the profiles of the fluid’s velocity determined with both solutions is also made. Furthermore, in order to study the influence of the material parameters, numerical simulations and graphical illustrations are used and useful conclusions are summarized.

    更新日期:2018-12-09
  • Structural, magnetic and magnetostrictive properties of Fe83Ga17 films with a Ti adhesion layer
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-12-08
    Jiaxing Shi, Cifu Lu, Hui Jiang, Wu Ming, Wenlong Hu, Yalong Zhao, Jiquan Wang, Mingming Li, Xing Mu, Jie Zhu

    In this study, Fe83Ga17 thin films are deposited on Si(100) and Si(111) substrates with a Ti layer by using DC magnetron sputtering. The addition of Ti layer does not significantly change the magnetic and magnetostrictive properties of the Fe-Ga film, however it can effectively prevent the abscission of film during heat treatment. The Fe83Ga17 films deposited on Si(100) and Ti/Si(100) have relatively small coercive forces, low saturation magnetic fields, and the magnetostriction curves are easily saturated in a low field. The magnetostriction of Fe83Ga17 on Ti/Si(100) can reach 105 ppm. The Fe83Ga17 thin films on Si(111) and Ti/Si(111) have large saturation magnetic fields (about 61Oe) and the magnetostriction curve shows linearity, which can be used in magnetic field detection, micro actuators and magnetoelectric (ME) devices. Dendritic domains and stripe domains are observed in these samples due to the influence of different internal stresses. After a vacuum heat treatment, the internal stress was released. At the same time, the structure of both the dendritic domains and stripe domains turns into a dot domain. The EBSD results show that annealed Fe-Ga films sputtered on a Ti layer have a very weak texture.

    更新日期:2018-12-09
  • Perpendicular magnetic anisotropy and tunneling conductivity of epitaxial cobalt-ferrite (001) films grown on nonmagnetic metal films
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-12-08
    Katsuyoshi Naruse, Masaaki Tanaka, Kosuke Nomura, Takuya Taniguchi, Syuta Honda, Teruo Ono, Ko Mibu

    We successfully fabricated perpendicularly magnetized cobalt-ferrite CoxFe3-xO4+δ (001) films on nonmagnetic metal TiN (001) films. We found that the in-plane lattice constant of the CoxFe3-xO4+δ (001) films was larger than the out-of-plane lattice constant. This lattice strain induced perpendicular magnetic anisotropy, and square hysteresis curves were observed in out-of-plane magnetic fields for the CoxFe3-xO4+δ (x=0.3∼0.6) films. With the decrease of the Co composition from x=1 to x=0, the CoxFe3-xO4+δ films approached not to conductive Fe3O4 but to insulating γ-Fe2O3 accompanying cation vacancies in the cubic spinel structure. The good tunneling conductivity character was observed for the CoxFe3-xO4+δ tunnel junctions. The results open up a possibility that insulating CoxFe3-xO4+δ films can be applied to elements of perpendicularly magnetized spintronics devices.

    更新日期:2018-12-09
  • Numerical method for analysis of the correlation between ferrofluid optical transmission and its intrinsic properties
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-12-08
    Á. Sanz-Felipe, J.C. Martín

    A numerical method to simulate the ferrofluid particle distribution evolution is presented. Also, the optical transmission of the distributions obtained is calculated by two numerical methods. The first one consists on a numerical propagation of an electromagnetic wave through the sample. The second one analyzes the aggregates’ mean length to obtain the optical transmission through a mixture law. As an illustration of the possibilities of the method developed, it is applied to analyze how ferrofluid optical transmission changes after magnetic field application depend on intrinsic properties of the colloid such as its nanoparticle concentration and surfactant repulsion represented by means of the final distances between consecutive particles forming chains. Changes in the attenuation factor of these samples show the trends expected from the Literature.

    更新日期:2018-12-09
  • Twisted magnetization states and inhomogeneous resonance modes in a Fe/Gd ferrimagnetic multilayer
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-12-08
    A.B. Drovosekov, A.O. Savitsky, D.I. Kholin, N.M. Kreines, V.V. Proglyado, M.V. Makarova, E.A. Kravtsov, V.V. Ustinov

    Static and dynamic magnetic properties of a ferrimagnetic Fe(35Å)/Gd(50Å)12 superlattice were investigated in a wide 4-300 K temperature range using magneto-optical Kerr effect (MOKE) and ferromagnetic resonance (FMR) techniques. The multilayer structure was sputtered on a transparent glass substrate which made it possible to perform MOKE measurements on both Fe and Gd terminated sides of the superlattice. These experiments allowed us to detect a transition between field-aligned and canted magnetic states on both sides of the film and to distinguish between the bulk and surface twisted phases of the superlattice. As a result, the experimental H-T magnetic phase diagram of the system was obtained. FMR studies at frequencies 7-36 GHz demonstrated a complex evolution of absorption spectra as temperature decreased from room down to 4 K. Two spectral branches were detected in the sample. Theoretical simulations show that the observed spectral branches correspond to different types of inhomogeneous resonance modes in the multilayer with non-uniform magnetization precession inside Gd layers.

    更新日期:2018-12-09
  • Origin of magnetization in diluted magnetic semiconductor GaGdAs monolayer and superlattice
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-12-06
    Hayato Miyagawa, Nakaba Funaki, Shyun Koshiba, Naoshi Takahashi, Yoshihiko Inada, Masaichiro Mizumaki, Naomi Kawamura, Motohiro Suzuki

    In this study, monolayer (ML)- and superlattice (SL)-diluted magnetic GaGdAs semiconductors are fabricated, and their electronic states are analyzed by x-ray absorption spectrum (XAS) and magnetic circular dichroism (MCD) by comparing with the values observed in case of macroscopic magnetization. The Gd magnetic moment per atom that was obtained from MCD exhibited a lower value than that obtained from a superconducting quantum interference device (SQUID) and tended to be larger in the SL structure as compared to the ML structure. We further observed that the Gd magnetic moment was enhanced by more than several tens of μB because of increasing carrier density by Si doping. The transmission electron microscopy images revealed dark regions with diameters of 2–3 nm, which were indicative of the high concentrations of Gd that further resulted in the formation of zincblend GaGdAs particles.

    更新日期:2018-12-07
  • Influence of crystal orientation on the magnetostriction behavior of Fe films formed on MgO single-crystal substrates
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-12-07
    Kana Serizawa, Mitsuru Ohtake, Tetsuroh Kawai, Masaaki Futamoto, Fumiyoshi Kirino, Nobuyuki Inaba

    Fe thin films are prepared on MgO substrates of (001), (110), and (111) orientations by ultra-high vacuum magnetron sputtering. The magnetostriction behaviors under rotating magnetic fields are observed by using a cantilever method. The relationship between in-plane magnetic anisotropy and magnetostriction behavior is investigated. An Fe(001)bcc single-crystal film is obtained on MgO(001) substrate. A four-fold symmetry in in-plane magnetic anisotropy is observed for the Fe(001)bcc film, where the easy magnetization directions are parallel to bcc[100] and bcc[010]. An Fe(211)bcc bi-crystalline film is formed on MgO(110) substrate and the film also shows an almost four-fold symmetric magnetic anisotropy. The reason is interpreted to be due to an influence of overlap of magnetic anisotropies of two bcc(211) variants with two effective easy magnetization directions which are obtained by projecting bcc[100] and bcc[010] on the bcc(211) plane. An Fe(110)bcc film is epitaxially grown on MgO(111) substrate with two types of variant with the crystallographic orientation relationships similar to Nishiyama-Wasserman and Kurdjumov-Sachs. The Fe(110) film shows an isotropic in-plane magnetic property due to an influence of the variant structure. Usual sinusoidal waveforms of magnetostriction are observed for the Fe(110) film. On the other hand, waveforms measured for the Fe(001) and the Fe(211) films are deformed from sinusoidal shape under low in-plane rotating magnetic fields and the magnetostriction behaviors are similar between the two films. Rectangular waveforms are observed for the bending parallel to easy magnetization directions, whereas triangular waveforms are recognized for the bending parallel to hard directions. The phenomenon is related to the direction difference between applied magnetic field and magnetization in magnetically unsaturated films with in-plane anisotropies. The magnetostriction behavior is influenced by the symmetry of in-plane magnetic anisotropy.

    更新日期:2018-12-07
  • The structural-phase state and magnetoresistive properties of thin film alloys obtained by co-evaporated Cu and Co
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-12-05
    I.O. Shpetnyi, D.M. Kondrakhova, S.I. Vorobiov, B. Scheibe, V.I. Grebinaha, D.O. Derecha, Yu.I. Gorobets, I.Yu. Protsenko

    This research presents the study on the structural-phase states and magnetoresistive properties of thin nanogranular film alloys based on Cu and Co with a total concentration of Co in the range of 15 ≤ x ≤ 71 at.%. The analyses for the unannealed and annealed thin films with a thickness d = 20 nm, have been performed. The films have been annealed in the temperature range from 300 to 800 K for 20 min. It found that the heat treatment within the range from 600 to 800 K led to an increase in the magnetoresistance and coercive force due to the growth of Co granules size under heat treatment and partial decomposition of the fcc-Cu(Co) solid solution. The highest magnitudes of the magnetoresistance were found in the as-deposited film alloys featured by the total concentration of Co x = 21 at.%, which consist of Cu(Co) solid solution made of fcc-Cu and superparamagnetic Co granules (size L = 2÷5 nm). Interestingly, the thin film alloys with an increased concentration of Co x ≥ 50 at.% exhibited anisotropic magnetoresistance.

    更新日期:2018-12-06
  • Separation of excitation and detection coils for in vivo detection of superparamagnetic iron oxide nanoparticles
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-12-05
    M.M. van de Loosdrecht, S. Waanders, H.J.G. Krooshoop, B. ten Haken

    A novel probe for laparoscopic in vivo detection of superparamagnetic iron oxide nanoparticles (SPIONs) has been developed. The main application for in vivo detection of SPIONs our research group aims at is sentinel node biopsy. This is a method to determine if a tumor has spread through the body, which helps to improve cancer patient care. The method we use to selectively detect SPIONs is Differential Magnetometry (DiffMag). DiffMag makes use of small magnetic field strengths in the mT range. For DiffMag, a handheld probe is used that contains excitation and detection coils. However, depth sensitivity of a handheld probe is restricted by the diameter of the coils. Therefore, excitation and detection coils are separated in our novel probe. As a result, excitation coils can be made large and placed underneath a patient to generate a sufficiently large volume for the excitation field. Detection coils are made small enough to be used in laparoscopic surgery. The main challenge of this setup is movement of detection coils with respect to excitation coils. Consequently, the detector signal is obscured by the excitation field, making it impossible to measure the tiny magnetic signature from SPIONs. To measure SPIONs, active compensation is used, which is a way to cancel the excitation field seen by the detection coils. SPIONs were measured in various amounts and at various distances from the excitation coils. Furthermore, SPIONs were measured in proximity to a surgical steel retractor, and 3L water. It is shown that small amounts of SPIONs (down to 25 μ g Fe) can be measured, and SPIONs can be measured up to 20 cm from the top of the excitation coil. Also, surgical steel, and diamagnetism of water – and thus of tissue – have minor influence on DiffMag measurements. In conclusion, these results make this novel probe geometry combined with DiffMag promising for laparoscopic sentinel node biopsy.

    更新日期:2018-12-06
  • Experimental and Numerical Analysis of the Magnetophoresis of Magnetic Nanoparticles under the Influence of Cylindrical Permanent Magnet
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-12-05
    Jiajia Sun, Zongqian Shi, Shuang Chen, Shenli Jia

    Dye-tracing and concentration-measuring experiments are carried out to investigate the magnetophoresis of magnetic nanoparticles (MNP) in the presence of an external cylindrical permanent magnet. The magnetophoresis of MNP, inducing an obvious forced-convective flowing of the carrier fluid, which can be observed by visualizing flowing of carrier fluid, results in a temporal and spatial variation of particle concentration. Moreover, in order to get insight into the physical mechanisms of magnetophoresis of MNP, a coupled particle-fluid analysis, in which the non-linear drift-diffusion differential equation is incorporated into the Navier-Stokes equation, is adopted to discuss the influence of particle-fluid interaction on the variation of particle concentration and the kinetics of carrier fluid. It is worth noting that the equivalent current source (ECS) method is adopted to obtain a closed-form field analysis, which provides exactly prediction of the Kelvin force and enables magnetophoretic analysis more efficient. In dye-tracing experiments, an obvious vortex can be observed as the methylene blue moves with the convection of carrier fluid. Furthermore, this phenomenon is also predicted by using the coupled particle-fluid model. A comparison between the experimental and numerical results shows that the hydrodynamic interactions between MNP and carrier fluid plays an important role in inducing forced-convective flowing of carrier fluid and enhancing the magnetophoresis of MNP. Furthermore, these results also denote that the coupled particle-fluid model provides a more efficient and accurate method in investigating the magnetophoresis of MNP.

    更新日期:2018-12-06
  • Control of magneto-static and -dynamic properties by stress tuning in Fe-Si-B amorphous microwires with fixed dimentions
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-12-06
    I. Baraban, S. Leble, L.V. Panina, V. Rodioniva

    The factors, which influence the internal stresses in glass coated amorphous microwires were discussed in this work in relation to the magnetization behaviour and domain wall propagation. The approach taking into account the technological parameters of manufacturing by Ulitovsky-Taylor method is presented. The magnetization process and domain wall dynamics in Fe77.5Si7.5B15 microwires produced under different conditions but with identical geometric parameters were investigated experimentally and analysed on the basis of internal stress formation in different microwire states: as prepared, after glass removal and after annealing. It is demonstrated that the residual stresses in wires of the same composition are not defined exclusively by their geometry but depend on the technological regime. The stress modification due to relaxing treatments also proceeds differently in wires produced under different conditions. These conclusions are evidenced by comparing the domain wall mobilities which strongly depend on the internal stress.

    更新日期:2018-12-06
  • Interlayer coupling-driven magnetic ordering and magnetization processes in ultrathin Au/Co/Mo/Co/Au film
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-12-06
    Z. Kurant, M. Tekielak, I. Sveklo, A. Wawro, A. Maziewski

    Interlayer magnetic coupling in an Au/Co/Mo/Co/Au system fabricated by molecular beam epitaxy was studied as a function of the thicknesses of the cobalt and molybdenum spacer layers (denoted as dCo and dMo, respectively). Magnetization processes and magnetic domain structures were investigated using magneto-optical techniques. In the investigated thickness ranges, various magnetization configurations of the Co layers were observed: (A) both perpendicular, (B) perpendicular and in-plane, and (C) both in-plane. The interlayer exchange coupling field HIEC was determined as a function of dMo. With increasing dMo, this coupling changed from antiferromagnetic with a huge coupling field of ≈0.27 T to ferromagnetic and again to antiferromagnetic. A coupling oscillation period of around 1.4 nm was deduced by comparing the experimental data with the Ruderman–Kittel–Kasuya–Yosida model. For configurations (B) and (C), oscillations of the saturation magnetic field HSAT(dMo) perpendicular to the sample plane were found. Simplified and precise analytical expressions for HSAT were proposed by considering HIEC as well as the uniaxial magnetic anisotropy of one and both magnetic layers, respectively. Magnetic ordering was numerically modeled taking into account the dependences of layer anisotropy and exchange coupling on dCo and dMo, respectively. This modeling well described the remanent magnetization map (dCo, dMo) determined using the polar Kerr effect. It is also shown that HIEC(dMo) induced magnetization reorientation from in-plane to out-of-plane or from out-of-plane to in-plane magnetization configurations and canted magnetization of the Co layers.

    更新日期:2018-12-06
  • Magnetic and Electrical Properties of Mn-Substituted (La0.85Ag0.15)CoO3 Compounds
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-12-06
    S.K. Srivastava, B. Samantaray, T. Bora, S. Ravi

    In this work, we have studied the influence of Mn substitution at the Co site of (La0.85Ag0.15)CoO3 on magnetic and electrical transport properties. Single phase samples of (La0.85Ag0.15)(Co1-yMny)O3 for y = 0, 0.05, 0.10, 0.15, 0.20, 0.30 and 0.40 have been prepared by solid state route. The X-ray diffraction (XRD) patterns recorded at room temperature show that these samples for y = 0 to 0.3 crystalize in rhombohedral structure with R 3 ¯ c space group, while for y = 0.4, it transforms into orthorhombic structure with Pbnm space group. The lattice parameters increase systematically with Mn concentration due to the substitution of larger Mn3+ ions at Co3+ site. Temperature variation of magnetization data and their analyses show that all samples exhibit ferromagnetic transition with a large increase in transition temperature (TC) upon Mn substitution, i.e. from 3.4 K for y = 0 to 211.0 K for y = 0.4. Such increase in TC is explained in terms of improved double exchange interactions across Co3+-O2-- Co4+ , Co3+- O2--Mn3+ and Mn3+-O2--Mn4+ networks. The presence of considerable irreversibility between zero field cooled and field cooled magnetization data and the lack of saturation of magnetization data even at 10 T field is explained in terms of domain-wall pinning effect and the presence of competing antiferromagnetic interaction. Eventhough the electrical resistivity falls several orders of magnitude upon Mn substitution, no metal-insulator transition is observed.

    更新日期:2018-12-06
  • Structural, magnetic and electric properties of multiferroic NiFe2O4-BaTiO3 composites
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-12-06
    Prakash Bongurala, Venkataiah Gorige

    The room-temperature magnetoelastic coupling has been demonstrated in (x)NiFe2O4+(1-x)BaTiO3 (where x = 0-1 with a difference of 0.1) composite system by investigating its structural, magnetic and ferroelectric properties. The samples were prepared by a standard solid-state reaction method and characterized by x-ray diffraction, backscattered scanning electron microscopy and energy dispersive x-ray spectroscopy techniques. The temperature dependent magnetization data clearly show the significant jumps in magnetization curves at structural phase transitions of BaTiO3, signifying the strain-mediated converse magnetoelectric (CME) coupling in NiFe2O4-BaTiO3 multiferroic system. The substantial changes observed in the values of obtained parameters from structural, magnetic and ferroelectric properties clearly ensuring the strain-mediated magnetoelectric (ME) as well as CME effects in this system. The present investigation indicates that the NiFe2O4-BaTiO3 composite system will be a potential candidate for the future low-power consumption device applications at room temperature.

    更新日期:2018-12-06
  • Presence of atomic disorder and its effect on the magnetic and electronic properties of NiCrGa half Heusler alloy
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-12-04
    Madhusmita Baral, M.K. Chattopadhyay, Ravindra Jangir, Aparna Chakrabarti, Tapas Ganguli

    Polycrystalline NiCrGa half Heusler alloy, which is predicted to be a half-metallic ferromagnet from first principles calculations, has been synthesized by arc meting technique and its structural, magnetic as well as the electronic properties have been studied. The measured x-ray diffraction (XRD) pattern shows the signature of a disordered structure. Magnetization and magnetoresistance measurements indicate a competition between ferromagnetic and antiferromagnetic correlations in the sample, with no evidence of long range magnetic order down to the lowest temperature (2 K) and highest magnetic field (70 kOe) studied. The experimentally observed structural and magnetic properties are found to be significantly different from the theoretically predicted properties of the ordered cubic C1b structure. To probe into the possibility of the presence of atomic disorder in the system, we have performed theoretical calculations using the spin-polarized-relativistic Korringa-Kohn-Rostoker method (SPR-KKR). By comparing the experimental data from XRD, magnetization, photoelectron spectroscopy measurements and theoretical calculations, we conclude that NiCrGa has significant amount of atomic disorder. Although, the ordered structure is energetically more stable than the disordered structures, we find that after synthesis, the system tends to stabilize in a disordered structure. The nature of the disorder has been ascertained from experiments and the corresponding electronic structure and magnetic properties have been obtained. With this atomic disorder present in the sample, the ferromagnetic ordering is disturbed and the spin polarization is consequently reduced.

    更新日期:2018-12-05
  • Study of Anisotropy of Magnetic Noise, Generated by Magnetic Particles in Geomagnetic Field
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-12-05
    M.A. Polikarpov, M.N. Ustinin, S.D. Rykunov, A.Y. Yurenya, S.P. Naurzakov, A.P. Grebenkin, V.Y. Panchenko

    Any existing method of visualization of magnetic nanoparticles in biological objects provides for imposing of an external magnetic field on the object under study. The field can considerably change the space distribution and properties of the nanomagnetic ensemble under study. In our work a SQUID-based magnetoencephalography device was used for the measurement of a magnetic noise generated by superparamagnetic nanoparticles based ferrofluid in the stationary standing vial without imposing of an external magnetic field. It was demonstrated that the ferrofluid generates spontaneous magnetic fields sufficient for its localization inside the experimental setup. Besides it was revealed that the spontaneous magnetic fields at certain frequencies have a strong spatial anisotropy. The detected effect can essentially increase the spatial resolution of the proposed method of visualization of magnetic nanoparticles in biological objects without using the external magnetic field.

    更新日期:2018-12-05
  • Structural, magnetic and magnetocaloric properties of La0.5Sm0.2Sr0.3Mn1-xFexO3 compounds with (0 ≤ x ≤ 0.15)
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-12-03
    Kh. Abdouli, W. Cherif, H. Omrani, M. Mansouri, M.A. Valent, M.P.F. Graça, L. Ktari

    We have investigated the effect of the substitution of the Mn ions by Fe ions on the structural, magnetic and magnetocaloric behaviors of La0.5Sm0.2Sr0.3Mn1-xFexO3 (0 ≤ x ≤ 0.15) perovskites. The nanocrystalline powders have been synthesized by self-combustion process. Rietveld refinement of fitted and observed X-ray diffractions patterns shows the formation of single-phase compositions with an orthorhombic crystal system (Pnma space group). The variation of magnetization (M) vs. temperature (T) under the field-cooled (FC) and zero-field-cooled (ZFC) modes reveals a ferromagnetic-paramagnetic transition at the Curie temperature (TC). The (TC) decreases linearly with increasing x and changes from 278 K for x = 0 to 94K for x = 0.15. Arrott plot analyses and a universal curve method were applied for studying the order of the magnetic transition in this system, found to be of second order. Besides, the magnetic entropy change and the related Relative Cooling Power (RCP) values, sensitive to Fe doping, were estimated. In the vicinity of TC, |-ΔSM| reached a maximum value of 3.06 J kg-1 K-1, 2.93 J kg-1 K-1, 2.22 J kg-1 K-1 and 0.77 J kg-1 K-1, whereas the RCP was found to be 268 J Kg-1, 280 J Kg-1, 285 J Kg-1 and 226 J Kg-1 for x = 0.00, 0.05, 0.10 and 0.15, respectively in a magnetic applied field of 5T. Through these results, La0.5Sm0.2Sr0.3Mn1-xFexO3 materials are strongly suggested for use as active refrigerants for magnetic refrigeration technology near room temperature.

    更新日期:2018-12-04
  • Effect of Cooling Rates on the Microstructure and Magnetic Properties of MnAl Permanent Magnetic Alloys
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-12-03
    Zhen Xiang, Xiao Wang, Yiming Song, Lunzhou Yu, Erbiao Cui, Baiwen Deng, Dan Batalu, Wei Lu

    In this work, the microstructure, phase transformation and magnetic properties of MnAl permanent magnetic alloys prepared by the melt-spinning technique were systematically investigated by tuning the cooling rate. It was shown that the MnAl microstructure, phase transformation and magnetic properties can be tailored by the copper roller speed. With increasing of the roller speed, the phase transformation from the γ2, β phases to the ε phase was observed. In addition, the variation of magnetic properties was attributed to the phase content and microstructure of the ferromagnetic τ phase in the MnAl alloys, being controlled by the cooling rate. As a result, the high-purity τ phase MnAl was obtained at a copper roller speed of 5 m/s, which exhibited a high magnetization of 118.2 emu/g. Therefore, this work can provide a method for the direct fabrication of the high-purity ferromagnetic τ phase MnAl alloy.

    更新日期:2018-12-04
  • Measurement independent magnetocaloric effect in Mn-rich Mn-Fe-Ni-Sn(Sb/In) Heusler alloys
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-12-04
    Arup Ghosh, Rajeev Rawat, Arpan Bhattacharyya, Guruprasad Mandal, A.K. Nigam, Sunil Nair

    We report a systematic study on the magneto-structural transition in Mn-rich Fe-doped Mn-Fe-Ni-Sn(Sb/In) Heusler alloys by keeping the total valence electron concentration (e/a ratio) fixed. The martensitic transition (MT) temperature is found to shift by following a proportional relationship with the e/a ratio of the magnetic elements alone. The magnetic entropy change (ΔSM) across MT for a selected sample (Mn49FeNi40Sn9In) has been estimated from three different measurement methods (isofield magnetization (M) vs temperature (T), isothermal M vs field (H) and heat capacity (HC) vs T). We observed that though the peak value of ΔSM changes with the measurement methods, the broadened shape of the ΔSM –T curves and the corresponding cooling power (∼140 Jkg-1) remains invariant. The equivalent adiabatic temperature change (ΔT) ∼ -2.6 K has been obtained from indirect measurements of ΔT. Moreover, an exchange bias field ∼ 783 Oe at 5 K and a magnetoresistance of -30% are also obtained in one of these materials.

    更新日期:2018-12-04
  • Spin wave propagation in three-dimensional magnonic crystals and coupled structures
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-12-04
    P.A. Popov, A.Yu. Sharaevskaya, E.N. Beginin, A.V. Sadovnikov, A.I. Stognij, D.V. Kalyabin, S.A. Nikitov

    We present three-dimensional (3D) model of periodic meander-shaped ferromagnetic films. Spin wave propagation in such films and vertically coupled structures was studied using micromagnetic modeling and theoretical plane wave method. Spin waves in these structures essentially propagate in film’s segments located at right angles with respect to each other. This makes really possible for the wave to propagate in three dimensions. We calculated internal effective magnetic fields and obtained spin wave dispersion in single and vertically coupled structures. Additionally, comparison of surface and volume spin waves propagation in such meander films was provided. Our results can be useful for magnonic logic elements development.

    更新日期:2018-12-04
  • Chemical, structural and magnetic properties of the Fe/Sb2Te3 interface
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-12-04
    E. Longo, C. Wiemer, R. Cecchini, M. Longo, A. Lamperti, A. Khanas, A. Zenkevich, M. Fanciulli, R. Mantovan

    Interfacing Topological Insulators (TI) with ferromagnetic (FM) layers is a promising route towards the next generation of ultra-low power spintronic devices based on charge-to-spin current conversion. Here, we present the Fe/Sb2Te3 interface structure, chemical composition and magnetic properties. Thin films (30 nm) of the topological insulator Sb2Te3 were synthesized by Metal Organic Chemical Vapor Deposition (MOCVD) at room temperature on Si/SiO2 substrates, then capped with a 57Fe(1 nm)/54Fe(10 nm) bilayer by Pulsed Laser Deposition (PLD) to allow interface-sensitive Conversion Electron Mössbauer Spectroscopy (CEMS). X-ray diffraction (XRD) showed the polycrystalline nature of both the Fe and Sb2Te3 layers. X-ray reflectivity (XRR) identified a non-trivial layered structure with the presence of an intermixed layer at the Fe/Sb2Te3 interface. Time-of-Flight Secondary Ion Mass Spectrometry (ToF SIMS) confirmed the partial elemental interdiffusion between the Fe and Sb2Te3 layers. Interface-sensitive CEMS evidenced that about a half of the 1-nm-thick 57Fe layer in contact with Sb2Te3 coordinates ferromagnetically, whereas the remaining paramagnetic fraction preferentially bonds with Te. The Fe/Sb2Te3 system was shown to have far from sharp interface, exhibiting a marked chemical reactivity already at room temperature. The tendency of Fe to preferentially bond with the chalcogenide element of topological insulators has been previously observed for the interface with Bi2Se3 and Bi2Te3, thus suggesting a possible universal behavior at the interface between Fe and chalcogenide-based TI.

    更新日期:2018-12-04
  • Study on recycling technology for waste MQ bonded Nd-Fe-B magnets
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-12-03
    Yu Zhang, Min Liu, Shuo Sun, Xiaowen Yin, Yuxia Yin, Jiangcheng Guo, Weiqiang Liu, Dongtao Zhang, Ming Yue

    A simple method is introduced to obtain recycled Nd-Fe-B powders from waste bonded Nd-Fe-B bulk magnets. The main difficulty of the recovery of waste MQ bonded Nd-Fe-B magnets is how to remove the epoxy resins between the magnetic particles and the oxide impurities on the surfaces of the waste magnetic powders. Mixed solvents of acetone, Dimethyl Formamide and N-butyl alcohol were used to dissolve the epoxy resins. Oxide impurities were removed using 0.5% acetic acid/acetone solutions. After these treatments, the carbon and oxygen contents were reduced from 21200 ppm to 9700 ppm, and from 11007 ppm to 8177 ppm, respectively. Under optimum processing conditions, the recycled magnetic powders possess improved magnetic properties with Ms of 151.5 emu/g, Mr of 98.0 emu/g, Hcj of 7.1 kOe, and (BH)max of 13.7 MGOe. These values, compared to the waste magnetic powders, represent increases of 21.2%, 18%, 0 and 34.3%, respectively.

    更新日期:2018-12-03
  • Spontaneous and induced magnetic phase transitions in Tb0.9Er0.1Ni5
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-12-03
    H.-J. Lee, Y.-N. Choi, A.V. Lukoyanov, E.G. Gerasimov, A.N. Pirogov

    Magnetic and neutron powder diffraction measurements have been carried out on Tb0.9Er0.1Ni5 intermetallic compound. The intermetallide crystallizes in the hexagonal CaCu5-type structure and possesses a long-range magnetic order at temperatures below 22 K. A fan- like magnetic structure is described by two propagation vectors: k1 = 0 and k2 = 2π/c(0, 0, 0.036), at 20 K. The total Tb-ion magnetic moment has the ferromagnetic and modulated components. The latter is a transverse spin wave. When the sample is cooled at a temperature below 8 K, the module of the k2 vector does not change and is equal to k2 = 2π/c(0, 0, 0.027). An “incommensurate – lock-in” magnetic transition takes place at 8 K. The k2 vector exhibits a temperature hysteresis of about (5 – 6) K, whereas the intensities of Bragg reflections and satellites do not show up appreciable changes. When an external magnetic field is applied to the sample, the satellites and the module of the k2 vector decrease, while the Bragg intensities increase. The sample becomes a ferromagnetic at a field of ∼2 kOe, and the Tb-ion magnetic moment is equal to 7.3 μB. A general notion of the Tb0.9Er0.1Ni5 magnetic state evolution with an external field is given using the field dependence of the background intensity in diffraction patterns. First principle calculations for TbNi5 and Tb0.9Er0.1Ni5 are performed including the 4f states into the orbital basis and accounting for strong electronic correlations and spin-orbital coupling. This allowed obtaining both spin and orbital moments of the effective Tb-ion moment and estimating also the value of Tb-Tb exchange interaction.

    更新日期:2018-12-03
  • Characterization of the Magnetic Phases of Holmium Nanofilms via Magnetic Neutron Scattering
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-12-03
    V.D. Mello, F.A.L. Santiago, D.H.A.L. Anselmo, M.S. Vasconcelos, N.S. Almeida

    Magnetic phases of holmium films are associated with the intensity of the magnetic neutron scattering. It is shown that each magnetic phase of the system (fan, helifan, spin-slip, helix and ferromagnetic) exhibits a characteristic profile of scattering which can be used as a fingerprint to identify it. In this paper, we present theoretical results obtained for holmium films 24 monolayers thick at a fixed temperature and in the presence of a dc magnetic field applied along the basal plane. A self-consistent local field algorithm was used to obtain the equilibrium configurations of the magnetic moments of the film and, with these results, the spin-spin correlation functions which determine the shape of the neutron scattering intensity were calculated.

    更新日期:2018-12-03
  • Impact of Gd ion substitution on the magneto-caloric effect of La0.6-xGdxSr0.4MnO3(x=0. 0.0125, 0.05,0.10) manganites
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-11-30
    M.H. Ehsani, T. Raoufi, F.S. Razavi

    The effect of slight changes of the chemical composition on Magneto-caloric properties of manganite was investigated on a series of ceramic nano-particles of La0.6-xGdxSr0.4MnO3 (x = 0.0, 0125, 0.05, 0.10) where they synthesized using the Sol-gel method. The X-ray powder diffraction data and the Rietveld refinement analysis indicated that the gradual replacement of La with Gd reduced the cell volume acting in a comparable manner to applying external pressure. Similarly, the magnetization measurements as a function of temperature on all La0.6-xGdxSr0.4MnO3 samples showed a ferromagnetic transition, in which the transition temperature reduced as x increased. The calculated magnetic entropies of all samples of La0.6-xGdxSr0.4MnO3 as a function of temperature suggest a magneto-caloric effect similar to that of pure Gd. These results provide evidence that La0.6-xGdxSr0.4MnO3 compounds have a potential for magnetic refrigeration application.

    更新日期:2018-12-01
  • Bismuth and antimony chalcogenides: peculiarities of electron density distribution, unusual magnetic properties and superconductivity
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-12-01
    V.G. Orlov, G.S. Sergeev, E.A. Kravchenko

    Electron band structure calculations and analysis of critical points parameters in the electron density distribution in Bi2Te3, Bi2Se3, Bi2S3, α-Bi2O3, Sb2Te3, Sb2Se3 and Sb2S3 at ambient and high pressures were performed to determine interrelations between the crystal structure, unusual physical (including magnetic and superconducting) properties and peculiarities in the electron density distribution. The programming code WIEN2k was used for band structure calculations. The previously found correlation between the superconducting transition temperature Tc and the electron density Laplacian value in the bond critical point with the highest electron density was confirmed by the calculations made for crystal structures under high pressure. The revealed parameters of bond critical points indicate the significant role of charge density fluctuations in the compounds studied. The 121, 123Sb NQR spin echo envelopes assigned to the ν1 transition (Δm=1/2-3/2) were measured for the two crystallographic positions of Sb atoms in the Sb2S3 structure. Unexpectedly deep oscillations of NQR spin echo envelopes were observed in very small (1-3 Oe) external magnetic fields, evidencing for the existence of local magnetic fields in Sb2S3 similar to those earlier observed in bismuth oxide compounds.

    更新日期:2018-12-01
  • Towards enhancing the magnetic properties by morphology control of ATiO3 (A = Mn, Fe, Ni) multiferroic materials
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-12-01
    R.A.P. Ribeiro, L.H.S. Lacerda, E. Longo, J. Andrés, S.R. de Lazaro

    Magnetic materials are of great interest due to their widespread applications in various technologies. Precise control of different aspects of the morphology and magnetic properties is a key aspect in establishing their relationshipwith material shapes and sizes. In this work, the density functional theory (DFT) is applied to investigate the surface structure and magnetic properties of low-index (110), (101), (100), (001), (111), (012) surfaces of ATiO3 (A = Mn, Fe, Ni) multiferroic materials. In particular, a theoretical approach, based on the Wulff construction and magnetization density (M) index, is applied to infer the relationship between the morphology and surface magnetism. The results indicate that the magnetic properties of ATiO3 materials can be controlled by the presence of exposed surfaces. In particular, the (001) and (111) surfaces are found to be adequate to enhance the superficial magnetism. The underlying reasons behind such mechanism are discussed from the perspective of uncompensated spins and charge-transfer processes along the exposed surfaces. This investigation suggests that the morphology-oriented ATiO3 materials are good candidates for superior multiferroic applications.

    更新日期:2018-12-01
  • Magnetic Fe3O4 Nanoparticles Coated by Natural Rubber Latex as MRI Contrast Agent
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-12-01
    Soudabeh Arsalani, Eder J. Guidelli, Matheus A. Silveira, Carlos E.G. Salmon, Jefferson F.D.F. Araujo, Antonio C. Bruno, Oswaldo Baffa

    Early detection is prerequisite for a successful cancer treatment. Recent advances in nanoscience and imaging technology allow the application of nanomaterials for early cancer diagnosis. Magnetic resonance imaging (MRI) has become one of the most extensively used and powerful tool for noninvasive clinical diagnosis. This work reports the synthesis and characterization of iron oxide nanoparticles coated with natural rubber latex (NRL), as well as their incorporation in a gelatin matrix to be used as an MRI contrast agent. Nanoparticles physical properties were characterized using X-ray diffraction (XRD), transmission electronic microscope (TEM), dynamic light scattering (DLS), magnetometry and MRI. XRD profiles indicated that magnetic nanoparticles (Fe3O4) with spinel structure were formed. TEM images showed the formation of iron oxide nanoparticles with average size about 9 to 14 nm, depending on the NRL concentration. Magnetization curves demonstrated iron oxide nanoparticles having superparamagnetic characteristics with increased magnetization as a function of NRL concentration. The zero-field cooling (ZFC) and field cooling (FC) curves show decreased blocking temperature upon coating magnetic nanoparticles with NRL. MRI results showed proton nuclear relaxivity ratios (r2/r1) of prepared MNPs significantly decreased by increasing the amount of NRL in the synthesis. Therefore, it can be concluded that NRL coated MNPs can be considered as an effective contrast agent for MRI applications.

    更新日期:2018-12-01
  • Hematite: Morin temperature of nanoparticles with different size
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-11-29
    D. Kubániová, L. Kubíčková, T. Kmječ, K. Závěta, D. Nižňanský, P.Brázda, M. Klementová, J. Kohout

    A spin-reorientation transition from a weakly ferromagnetic (WF) to an antiferromagnetic (AF) spin ordering in hematite (α-Fe2O3) during cooling occurs at Morin temperature (TM ∼264 K for bulk). The transition is strongly size dependent and TM generally decreases with the decreasing volume of the particles. For particles smaller than approximately ∼20 nm, the Morin transition may be even suppressed and disappears entirely as near-surface spins deviate strongly from the antiferromagnetic easy axis. We report an investigation on nanoparticles prepared by hydrothermal method and sol-gel technique (in silica) of pure α-Fe2O3 phase as confirmed by XRD (space group R-3c, lattice parameters a = 5.038(2) Å, c = 13.772(12) Å) differing in the median size derived by TEM: 5.6 nm, 26 nm, 42nm and 103 nm. By means of Mössbauer spectra acquired between 4.2 and 300 K, we determined the relative concentrations of magnetic phases (WF and AF) within the 57Fe enriched sample and searched for the best finite-scaling theoretical model (mean-field, 3D Heisenberg, Ising) describing the derived size dependence of Morin temperature of the nanoparticles with a log-normal size distribution. The comparison of relevant parameters derived from the fit of experimental data by theoretical model is consistent with the 3D Heisenberg model with scaling parameter λ=1.4, Morin temperature of bulk material TM(∞) = 265(1) K and correlation length ξ0 = 8.1(2) nm or Ising model with λ=1.6, TM(∞) = 265(1) K and ξ0 = 9.4(2) nm.

    更新日期:2018-11-30
  • Ferromagnetic long-range ordering in nano-crystalline La0.7Ca0.3Mn1-xNixO3 (x=0, 0.02) manganites
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-11-29
    A. Gómez, J.L. Izquierdo, I. Supelano, C.A. Parra, E. Chavarriaga, O. Moran

    Nanosized La0.7Ca0.3Mn1-xNixO3 (x=0, 0.02) manganites were synthesized via the auto-combustion method. The critical behavior of these samples was then carefully investigated by analyzing the results of static magnetic measurements near their critical temperatures. The samples exhibited second-order phase transition, and the effect of Ni doping was to lower the critical temperature. The analysis of the experimental data was carried out by means of various techniques, such as modified Arrott plots, the Kouvel-Fisher method, and critical isotherm analysis, which revealed that the values of the critical exponents β, γ, and δ are close to those theoretically predicted by mean-field theory. By using the Widom scaling relation and the universal scaling hypothesis, the dependability of the obtained values of the critical exponents was confirmed. Moreover, the temperature dependence of the spontaneous magnetization was estimated from the analysis of the variation of the magnetic entropy change with the magnetization within the framework of mean-field theory. Interestingly, the spontaneous magnetization determined from the entropy change and that obtained from classical extrapolation of the Arrott curves displayed high concordance. These results strongly suggested that the interactions among spins in the investigated compound are long-range.

    更新日期:2018-11-30
  • Magnetic properties and heating efficacy of magnesium doped magnetite nanoparticles obtained by co-precipitation method
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-11-30
    Vladan Kusigerski, Erzsebet Illes, Jovan Blanusa, Saso Gyergyek, Marko Boskovic, Marija Perovic, Vojislav Spasojevic

    Ferrofluids based on magnesium substituted magnetite nanoparticles MgxFe3-xO4 (x=0.1; 0.2; 0.4) were synthesised by a chemical co-precipitation method. Their physical properties have been compared with those of the magnetite based ferrofluid obtained by the same synthesis route. Both XRD and TEM studies showed particle size decrease with the increased Mg content while DLS experiments pointed to the more prominent aggregation of Mg-containing nanoparticles. Magnetic properties investigation conducted on the powder (i.e. dried) specimens showed decrease of magnetization values with increased Mg content except for the lowest concentration of x=0.1 where substantial saturation magnetization rise of about 40% was recorded at room temperature. Heating abilities of the studied ferrofluids under the applied AC fields (SAR values) also showed decreasing trend with the increased Mg content even for x=0.1 sample despite its elevated magnetization value. This trend has been understood as a consequence of the changed intrinsic nanoparticle properties such as size and magnetic anisotropy, as well as contribution of a collective behaviour due to an increased nanoparticle aggregation in Mg-doped systems.

    更新日期:2018-11-30
  • Preparation of rGO/CIP/PVA composites and their microwave absorption properties
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-11-30
    Zhang Qi, Liu Chunbo, Wu Zhuang, Yang Yang, Xie Zhiyong

    The design of advanced structures to adjust the dielectric constant and permeability is an effective way to improve the absorbing properties of the materials. The carbonyl iron powder (CIP) was coated with PVA after ball milling, and graphene oxide (GO) was evenly dispersed on the surface. Then GO was reduced by heat treatment, and the composite material was obtained. The electromagnetic parameters of the as-prepared rGO/CIP/PVA composites, such as relative complex permittivity and permeability, were investigated in the frequency range of 2.0–18.0 GHz, and their loss mechanism were investigated too. Under the premise of not changing the magnetic loss, dispersed rGO can effectively improve the dielectric loss of the composite material and thus improve the microwave absorption capability. The effective absorbing width (reflection loss lower than −10 dB) of composite materials with GO and the prepared CIP/PVA composite at 1 mg/g was about 8.4 GHz.

    更新日期:2018-11-30
  • Surface spin waves in coupled easy-axis antiferromagnetics films
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-11-30
    A.Yu. Sharaevskaya, D.V. Kalyabin, E.N. Beginin, Yu.K. Fetisov, S.A. Nikitov

    We present results of studying properties of surface spin waves in vertically coupled antiferromagnetic films with easy-axis anisotropy. The dispersion curves and frequency region of the existence of the surface magnetostatic waves are obtained using theoretical model for different antiferromagnetic materials. This study was carried out by solving the dispersion relation for the surface magnetostatic waves. Behavior of two type of dispersion on the value of coupling parameter is investigated. We conclude, that results have potential applications for antiferromagnetic THz spintronics.

    更新日期:2018-11-30
  • Magnetic field dependence of Griffith phase and critical behavior in La0.8Ca0.2MnO3 nanoparticles
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-11-28
    P.T. Phong, L.T.T. Ngan, L.V. Bau, N.X. Phuc, P.H. Nam, L.T.H. Phong, N.V. Dang, In-Ja Lee

    In this work, the La0.8Ca0.2MnO3 nanoparticles of ∼30 nm were prepared by a sol-gel method, and their magnetic properties were investigated. The sample shows a paramagnetic-to-ferromagnetic phase transition at about 214 K. The Griffiths phase, which is identified by the downturn of the inverse susceptibility versus temperature plot from the Curie-Weiss law, is suppressed with the increase of the applied magnetic field strength such as 10 kOe. From the study of magnetic properties in terms of Arrot plots, the nature of magnetic transitions is found to be of second order. The critical behavior of La0.8Ca0.2MnO3 nanoparticles was studied around its Curie temperature. The estimated critical exponents were close to those expected for mean-field model. These critical exponents fulfill the Widom scaling relation, implying the reliability of our values.

    更新日期:2018-11-28
  • Coexistence of Ferromagnetism and Spin glass state in YbNi2 nanoparticles
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-11-28
    D.P. Rojas, L. Fernández Barquín, J.I. Espeso, J. Rodríguez Fernández, D. Alba Venero, J.A. Gallastegui, G.R. Castro, V.A. Ivanshin

    We report changes on the magnetic behavior of the Heavy-Fermion ferromagnetic YbNi2 alloy when reducing the size of the particles to the nanometer scale by high-energy ball milling. The milling process induces a reduction on the particle size of the bulk alloy down to 10 (2) nm and a lattice strain of 1.8 (2)%, for 30 h of milling time, as calculated from the x-ray diffraction data. The ferromagnetic transition at TC =10.5 K in the bulk alloy tends to disappear whereas other magnetic transitions arise at lower temperatures with the milling process. The AC magnetic susceptibility of the 30 h milled sample shows a frequency independent peak at 3 K, in a wide range of frequencies, consistent neither with superparamagnetic nor simple freezing of the magnetic moments, and as expected for a ferromagnetic behavior. However, from the specific heat measurements in the 30 h milled sample, a peak at 3.6 K is shifted respect to that observed in the AC magnetic susceptibility, as found in spin glasses. Additionally, the specific heat on nanometric samples show reduced magnetic contributions respect to the bulk alloy with Δcmax around 0.45 J/molK. The results are explained by the influence of magnetic inhomogeneities and disorder of the alloys enhanced by the milling process in the ensemble of nanoparticles.

    更新日期:2018-11-28
  • The Effects of Tb Doped ZnO nanorod: an EPR Study
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-11-28
    L. Arda

    Structural and magnetic behaviors were studied and correlated with each other for Zn1−xTbxO nanorods synthesized by hydrothermal method varying x values from 0.01 to 0.05 with 0.01 step increment. The structural properties of Zn1−xTbxO nanorods were determined by X-ray diffraction tool. All nanorods were found as a single phase with ZnO wurtzite hexagonal structure. The concentration-dependent of lattice parameters, cell volumes, microstrain, stress, dislocation density, the locality of the atoms and their displacements, and bond length in Zn1-xTbxO (where x=0.0, 0.01, 0.02, 0.03, 0.04, and 0.05) structures were detailed. The particles with varying magnifications were observed as random agglomeration using Scanning Electron Microscope measurement tool. ESR spectra of Zn1-xTbxO were collected at room temperature on a Bruker EMX model X-band spectrometer operating at a frequency of 9.71 GHz. ESR measurements have been performed and analyzed through concentration dependence of the g-factor and the line-widths of pike to pike (ΔHPP) of ESR spectra. Experimental and fitting X band ESR spectra of Tb doped ZnO nanorods with a different doping concentration of Tb recorded at room temperature were presented.

    更新日期:2018-11-28
  • DC magnetic characterization and pinning analysis on Nd1.85Ce0.15CuO4 cuprate superconductor
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-11-27
    A. Galluzzi, A. Nigro, R. Fittipaldi, A. Guarino, S. Pace, M. Polichetti

    We report the analysis of the magnetic response detected on the cuprate superconductor Nd1.85Ce0.15CuO4. In particular the magnetic behavior of the sample has been studied by means of DC magnetization measurements as a function of the temperature (T) and DC magnetic field (H). The superconducting critical temperature Tc has been obtained by analyzing the m(T) curve performed in Zero Field Cooling-Field Cooling conditions. Moreover, the m(T) curve shows the presence of a magnetic background for temperatures above Tc. By considering the superconducting m(H) hysteresis loop at different temperatures, it can be noted that the width of the curves appears narrow corresponding to a weak superconductivity. This is confirmed by the field dependence of the critical current densities Jc extracted from the superconducting hysteresis loops m(H) at different temperatures within the Bean critical state model. In fact, at the lowest measurement temperature, Jc is close to zero already at low magnetic fields. Nevertheless, by means of the temperature dependence of Jc, the sample shows a strong pinning behavior that can open perspectives for future improvement in the fabrication of this material.

    更新日期:2018-11-28
  • Comparative Study of Structural, Magnetic and Dielectric Properties of CoFe2O4 @ BiFeO3 and BiFeO3@ CoFe2O4 Core-Shell Nanocomposites
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-11-27
    Nidhi Sheoran, Vinod Kumar, Ashok Kumar

    Nano-sized CoFe2O4 (CFO), BiFeO3(BFO) and their core-shell composites BFO@CFO and CFO@BFO were synthesized by chemical co-precipitation method. X-ray diffraction pattern confirmed the crystallinity and phase formation of bare CFO, BFO and their core-shell composites. Morphology and core-shell nature of these nanoparticles is justified by field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM). Magnetization curve showed the weak ferromagnetic behaviour of BFO. Typical ferrimagnetic behaviour is shown by bare CFO and core-shell nanocomposites. The value of maximum magnetization, remanence magnetization and coercivity of CFO@ BFO were found to be greater than the BFO@ CFO. Also, CFO@ BFO showed the highest value of dielectric constant in the frequency range of 104-106 Hz. Dielectric constant versus temperature curve of BFO and core-shell composites exhibit incongruity close to the antiferromagnetic transition temperature (370 OC) of BFO indicating presence of magnetoelectric (ME) coupling.

    更新日期:2018-11-28
Some contents have been Reproduced with permission of the American Chemical Society.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
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